Mariano Rivera announced his looming retirement from baseball Saturday in Florida, as expected, and the lack of surprise was appropriate. Predictability has been the defining characteristic of the Mariano Rivera experience—the knowledge that calling upon the lean relief pitcher was essentially to end a ballgame several outs early, extinguishing an opponent and giving the crowd a few extra minutes to gather personal effects. Rivera was not perfect, as they know in Arizona and Boston, but he was pretty close, and during an 18-year career his statistics have piled into something unprecedented, an overwhelming case of Rivera being one of the most dominant pitchers—no, players—ever. When he departs at the end of this 2013 season, he doesn't need to unlace his spikes. Metallica pumping, the Sandman can walk directly to Cooperstown, N.Y., home of the Baseball Hall of Fame, where the only suspense will be whether or not Rivera is elected unanimously on the first ballot. This has never happened. Baseball is stubborn, full of musty self-regard. Zeus would get snubbed a few votes. One hundred percent may elude Rivera, too.

Rivera began his morning farewell news conference with a joke, telling the assembled reporters and team personnel that he was grateful to Yankees general manager Brian Cashman for a two-year-contract extension carrying into 2015. Cashman, his leg crumpled from a sky diving mishap, played along, offering a thumbs-up from a wheelchair. A joke from Mo! It was a snazzy change-up from a serious man. Retirement announcements can be mushy, lugubrious episodes—an athlete's first public confrontation of his playing perishability—but Rivera appeared relaxed and composed during the telecast. He is playing one more season, after all. He seemed to well up, but he did not cry. He spoke of his recovery from the knee injury he suffered in 2012, and how he didn't want to leave like that. He said he "had a few bullets left," and "I'm going to use them well." After a while it began to resemble less of a goodbye than a reassertion of purpose. Look at him! Did this man look 43? Rivera never was going to leave, was he?

But he is leaving, he promised. Mo, what tells you the tank is almost empty, he was asked. "I'm telling you it's empty," he said, drolly. "I think that's enough." More laughs! He said he dreamed of wrapping it up atop the mound for another Yankee World Series. And though the announcement brought back a rush of memories, what was essentially left unspoken was perhaps the most remarkable accomplishment of Rivera's career.

Its dignity.

Dignity is an unusual, evasive value in modern sports. There's no metric for it, no statistical standard. It's a little old-fashioned-sounding, almost corny, and it's unclear how much dignity matters anymore. Dignity will not get you a high-profile apparel contract or a magazine cover and it does not ensure a post-playing career as a blustering talking head. One could argue that dignity makes it a little harder to secure those things, because part of what dignity means is not calling attention to oneself, because making a big deal about yourself is undignified. Truth be told, if you want all of these things, you might want to avoid dignity. Dignity is a little boring.

But it shouldn't be, because dignity is hard. And it's freakishly hard to pull off in a sawmill like New York, which strips apart its sports icons from the outside in, questioning first the performance, then the commitment, and then the character, almost reveling as it spits out the bones. Even the best athletes seldom last a season there without a flurry of real or imagined chaos. Rising and falling, humiliation and redemption—it's all part of the narrative structure of playing games in New York, the brutal sport within the sport.

And yet Rivera has thrived for nearly two decades, playing for the most comically demanding New York franchise of them all. Yes, New York's infatuation with its New York-ness is hopeless and mostly annoying, but in this instance it is really true: There is no hothouse quite like the Yankee hothouse, and to remain emotionally intact, as Rivera has done for so many years, should be held up as some kind of marvel alongside those freakish numbers for saves (608) and postseason earned-run average (0.70). Like his loyal teammate Derek Jeter, who is narrowing in on age 40, Rivera will be remembered for the way he stayed one step ahead of an unforgiving town, carrying himself with a humility that seemed hard-wired into his DNA. (When the talk at the news conference turned to Rivera's place as one of the greatest ever, he would indulge none of it, saying he only wanted to be remembered for making the players around him better.)

Athletes are held to high standards, this is true. But they also get so much praise for doing things that ordinary people just do—look at the gooey rapture over seeing the Yankees assemble as a team in the back of Rivera's news conference, as if it was some grand act, and not basic, expected human courtesy for a teammate. Rivera, who by baseball's declaration will be the last player to wear Jackie Robinson's No. 42, is a reminder of how things are to be done. Rivera is not the type to want a glitzy rocking-chair farewell tour, but the Yankees said he intends to take a little time in each farewell stop to meet with people who love baseball as he does—a longtime usher, or a family that has traveled from far away. These individuals do not have to be admirers of Rivera or even Yankee fans.

It is a small gesture, and yet more proof of an all-timer who recognizes what baseball is—a game that perseveres because its history is bigger than one individual, even one who was among its biggest. Mariano Rivera has a final season to go. Perhaps it will be what's expected: more of the brilliant, old same.

This copy is for your personal, non-commercial use only. Distribution and use of this material are governed by our Subscriber Agreement and by copyright law. For non-personal use or to order multiple copies, please contact Dow Jones Reprints at 1-800-843-0008 or visit www.djreprints.com.